Conventionally, according to JP2014-001954A, it is known that a flowing measuring device includes a housing and a flow sensing chip. The housing includes a bypass passage introducing a part of an air flowing through an intake air channel of an internal combustion engine. The flow sensing chip is located in the bypass passage and includes a sensing surface portion generating an electrical signal in response to a flow volume of the air in the intake air channel by a heat transmission between the sensing surface portion and the air flowing through the bypass passage.
The sensing surface portion is located in a direction parallel to a flowing direction of a flow of the air flowing through the bypass passage. The bypass passage is throttled by a throttle portion such that a cross-sectional area of the bypass passage perpendicular to the flowing direction decreases in accordance with a decrease in distance from a gravity center of the sensing surface portion to a center of the cross-sectional area in the direction parallel to the flowing direction.
Thus, when the flow volume of the air in the intake air channel is relatively small, a flow rate of the air at the sensing surface portion can be sufficiently ensured, a heat transmission performance and a sensing accuracy of the flow volume can be ensured. However, when a flowing passage wall changes at the throttle portion at a sharp angle, a vortex or a separation is generated in the flow of the air in the vicinity of the throttle portion, and the flow of the air is disturbed to cancel a straightening function.
When the vortex is generated in the vicinity of the throttle portion, a flow of the air flowing in a reverse direction that is opposite to the flowing direction is generated. In this case, a pressure loss is generated in the bypass passage, and the flow volume at the sensing surface portion is decreased. Further, when the vortex is generated in the vicinity of the throttle portion in a case where the throttle portion is close to the sensing surface portion and a pulse flow is generated in response to an operation of a piston of the internal combustion engine, the vortex reaches the sensing surface portion to lead to a sensing error.